U.S. patent number 9,278,681 [Application Number 13/837,680] was granted by the patent office on 2016-03-08 for hybrid electric vehicle driveline active damping and transient smoothness control.
This patent grant is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. The grantee listed for this patent is Ford Global Technologies, LLC. Invention is credited to Jonathan Andrew Butcher, Thomas Chrostowski, Jeffrey Allen Doering, Ming Lang Kuang, Wei Liang, Fazal Urrahman Syed, Xiaoyong Wang.
United States Patent |
9,278,681 |
Liang , et al. |
March 8, 2016 |
Hybrid electric vehicle driveline active damping and transient
smoothness control
Abstract
A method and system for controlling a hybrid electric vehicle
include controlling torque in a traction motor in response to a
provisional motor torque that has been adjusted based on a
difference between a measured traction motor speed and a calculated
vehicle speed and filtered to attenuate a resonant driveline
frequency.
Inventors: |
Liang; Wei (Farmington Hills,
MI), Doering; Jeffrey Allen (Canton, MI), Wang;
Xiaoyong (Novi, MI), Chrostowski; Thomas (Chesterfield,
MI), Butcher; Jonathan Andrew (Farmington, MI), Kuang;
Ming Lang (Canton, MI), Syed; Fazal Urrahman (Canton,
MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Assignee: |
FORD GLOBAL TECHNOLOGIES, LLC
(Dearborn, MI)
|
Family
ID: |
51419327 |
Appl.
No.: |
13/837,680 |
Filed: |
March 15, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140277875 A1 |
Sep 18, 2014 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60W
10/06 (20130101); B60W 10/08 (20130101); B60K
6/445 (20130101); B60W 20/17 (20160101); B60W
20/00 (20130101); B60W 30/20 (20130101); B60W
2710/083 (20130101); Y02T 10/6239 (20130101); Y02T
10/7258 (20130101); Y10S 903/93 (20130101); Y02T
10/62 (20130101); Y02T 10/72 (20130101) |
Current International
Class: |
B60W
20/00 (20060101); B60K 6/445 (20071001); B60W
10/08 (20060101); B60W 10/06 (20060101); B60W
30/20 (20060101) |
Field of
Search: |
;701/22,61 ;180/381 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Fazal U. Syed, Ming L. Kuang, and Hao Ying, Active Damping
Wheel-Torque Control System to Reduce Driveline Oscillations in a
Power-Split Hybrid Electric Vehicle, IEEE Transactions on Vehicular
Technology, Nov. 2009, pp. 4769-4785, vol. 58, No. 9. cited by
applicant.
|
Primary Examiner: Holloway; Jason
Attorney, Agent or Firm: Kelley; David B. Brooks Kushman
P.C.
Claims
What is claimed is:
1. A method of controlling a hybrid electric vehicle comprising:
commanding a traction motor to supply a traction motor torque in
response to a provisional motor torque, the provisional motor
torque being adjusted by a PD control based on a difference between
a measured traction motor speed and a calculated vehicle speed and
filtered by a filter to attenuate a driveline natural resonant
frequency, the PD control being distinct from the filter.
2. The method of claim 1, wherein the calculated vehicle speed is
based on an average of wheel speed signals.
3. The method of claim 2, wherein the wheel speed signals are
received from an antilock brake system control module.
4. The method of claim 1, wherein the calculated vehicle speed is
based on a measured motor speed filtered through a low pass
filter.
5. The method of claim 1, wherein the provisional motor torque is
generated in response to an engine start event.
6. The method of claim 1, wherein the provisional motor torque is
generated in response to a change in driver torque request.
7. A hybrid vehicle controller configured to receive a torque
request and output a commanded motor torque, the controller
comprising control logic that controls motor torque based on a
target torque, the target torque being filtered by a filter to
attenuate a driveline natural resonant frequency and adjusted by a
PD control based on a difference of a measured motor speed and a
calculated vehicle speed, the filter being distinct from the PD
control.
8. The controller of claim 7, wherein the control logic comprises a
band stop filter that filters the target torque.
9. The controller of claim 7, wherein the control logic comprises a
band pass filter that filters the target torque.
10. The controller of claim 7, wherein the calculated vehicle speed
is based on an average of wheel speed signals.
11. The controller of claim 10, wherein the wheel speed signals are
received from an antilock brake system control module.
12. The controller of claim 7, wherein the calculated vehicle speed
is based on a measured motor speed filtered through a low pass
filter.
13. The controller of claim 7, wherein the control logic comprises
a closed loop controller that adjusts the commanded torque based on
a difference between a measured motor speed and a calculated
vehicle speed in a feedback path.
14. The controller of claim 13, wherein the closed loop controller
includes a feedforward loop that filters the commanded motor torque
to remove frequency components related to the driveline natural
resonant frequency in the feedforward path.
15. The controller of claim 13, wherein the closed loop controller
filters the commanded motor torque to remove frequency components
related to the driveline natural resonant frequency in the feedback
path.
16. A hybrid vehicle comprising: a motor drivably connected to
traction wheels by a driveline having a natural resonant frequency;
and a motor controller configured to control motor torque in
response to a provisional motor torque, the provisional motor
torque being filtered by a filter to attenuate a driveline resonant
frequency and damped by a PD control, distinct from the filter,
based on a difference of a measured motor speed and a calculated
vehicle speed.
17. The hybrid vehicle of claim 16, wherein the motor controller
filters the provisional motor torque using a band stop filter to
remove poles of the driveline natural resonant frequency and
introduce a pair of well-damped poles at another frequency.
18. The hybrid vehicle of claim 16, wherein the calculated vehicle
speed is based on an average of wheel speed signals.
19. The hybrid vehicle of claim 18, wherein the wheel speed signals
are received from an antilock brake system control module.
20. The hybrid vehicle of claim 16, wherein the calculated vehicle
speed is based on a measured motor speed filtered through a low
pass filter.
Description
TECHNICAL FIELD
This disclosure relates to active damping and transient smoothness
control in hybrid electric vehicles.
BACKGROUND
Hybrid Electric Vehicles (HEVs) may use various types of powertrain
architectures to provide parallel, series, or a combination to
transfer torque from two or more sources to the traction wheels. A
power split architecture combines the driving torque generated by
the engine and the torque generated by one or more electric
machines in various operating modes. A representative power split
architecture is illustrated in FIG. 1. The two electric machines,
referred to as the motor and the generator, may be implemented by
permanent-magnet AC motors with three-phase current input. The
engine and the generator may be connected by a planetary gear set
with the engine crankshaft connected to the carrier and the
generator rotor connected to the sun gear. The gear on the motor
output shaft may be meshed to the counter shaft with a fixed ratio.
The ring gear may also be connected to the counter shaft in a fixed
ratio arrangement.
In this example, the motor is connected to the driveline through
the countershaft in parallel to the engine-sourced torque output
from the ring gear. The main functions of the motor include: 1.
Drive the vehicle in electric drive mode by supplying full required
torque; 2. Compensate the ring gear torque output based on driver
commands; and 3. Damp driveline oscillation.
Vehicle drivability, including smooth vehicle operation, is a
challenging issue for all types of automotive implementations.
Driveline resonance is one of the major reasons that a driver feels
unsmooth behavior during accelerations and decelerations with fast
torque changes. As such, increasing damping around the driveline
resonant frequency is a typical task for all types of automotive
powertrain controls. Automatic transmissions with hydraulic torque
converters have a large natural viscous damping effect due to the
torque transfer loss on the fluid. In HEV applications that do not
include a torque converter or similar device, this natural damping
effect is diminished. The resonant mode can be excited by the motor
torque input due to the fast response of the electric machines and
the small damping ratio in the mechanical driveline. The transient
smoothness is largely dependent upon a well-designed control
system.
SUMMARY
A method of controlling a hybrid electric vehicle comprises
controlling torque in a traction motor in response to a provisional
motor torque that has been adjusted based on a difference between a
measured traction motor speed and a calculated vehicle speed and
filtered to cancel poles of a resonant driveline frequency. The
calculated vehicle speed may be based on an average of wheel speed
signals, which may be received from an antilock brake system
control module. The calculated vehicle speed may alternatively be
based on a measured motor speed that has been filtered through a
low pass filter. The provisional motor torque may be generated in
response to a vehicle start event. The provisional torque may also
be generated in response to a change in a driver torque
request.
An embodiment of a hybrid vehicle controller according to the
present disclosure is configured to receive a torque request and
output a commanded motor torque. The controller comprises control
logic that filters a target torque to attenuate a driveline
resonant frequency, adjusts the target torque based on a difference
of a measured motor speed and a calculated vehicle speed, and
generates a commanded motor torque based on the filtered and
adjusted torque.
In some embodiments of a controller according to the present
disclosure, the control logic that filters the target torque may
include a band stop filter. The calculated vehicle speed may be
based on an average of wheel speed signals, or it may be calculated
based on a measured motor speed filtered through a low pass filter.
If the calculated vehicle speed is based on an average of wheel
speed signals, the wheel speed signals may be received from an
antilock brake system control module. In some embodiments, the
control logic that adjusts the commanded torque based on the
difference of a measured motor speed and a calculated vehicle speed
may be implemented in a feedback path. In such embodiments, the
control logic that filters the commanded motor torque to remove
frequency components may be implemented in a feedforward path or in
a feedback path.
An embodiment of a hybrid vehicle according to the present
disclosure comprises traction wheels, a motor drivably connected to
the traction wheels by a driveline having a resonant frequency, and
a motor controller. The motor controller is configured to generate
a provisional motor torque, filter the provisional motor torque to
attenuate a driveline resonant frequency, damp the provisional
motor torque as a function of a difference of a measured motor
speed and a calculated vehicle speed, generate a commanded torque
based on the filtered and damped motor torque, and provide the
commanded torque to the motor. Filtering the provisional motor
torque may include using a band stop filter to remove the poles of
the driveline resonant frequency and introduce a pair of
well-damped poles at another frequency. The calculated vehicle
speed may be based on an average of wheel speed signals, or it may
be calculated based on a measured motor speed filtered through a
low pass filter. If the calculated vehicle speed is based on an
average of wheel speed signals, the wheel speed signals may be
received from an antilock brake system control module.
Embodiments according to the present disclosure provide a number of
advantages. For example, the present disclosure provides a control
system for an HEV that can increase the robustness of the motor
torque control by removing the driveline resonant frequency from a
motor torque command to improve drivability.
The above advantage and other advantages and features of the
present disclosure will be readily apparent from the following
detailed description of the preferred embodiments when taken in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a power split architecture for a HEV in
schematic form.
FIG. 2 is a block diagram of an HEV according to one embodiment of
the present disclosure.
FIG. 3 is a flowchart illustrating an algorithm for controlling
motor torque in an HEV according to one embodiment of the present
disclosure.
FIG. 4 illustrates a control for active damping of motor torque
according to one embodiment of the present disclosure.
FIG. 5 illustrates methods for calculating vehicle speeds.
FIG. 6 illustrates a control for damping motor torque having a
filter in a feedforward path.
FIG. 7 illustrates a control for damping motor torque having a
filter in a feedback path.
DETAILED DESCRIPTION
As those of ordinary skill in the art will understand, various
features of the present invention as illustrated and described with
reference to any of the Figures may be combined with features
illustrated in one or more other Figures to produce embodiments of
the present disclosure that are not explicitly illustrated or
described. The combinations of features illustrated provide
representative embodiments for typical applications. However,
various combinations and modifications of the features consistent
with the teachings of the present disclosure may be desired for
particular applications or implementations.
Referring now to FIG. 1, an HEV may have a power split architecture
as illustrated. In such an HEV, the motor torque may be used for
damping by taking advantage of its higher bandwidth compared to the
combustion engine. An active damping (anti-jerky, anti-shuffle)
control is desired for smooth operation.
In this configuration, the ring gear torque can be used by the
motor torque controller for torque compensation. In steady state
operation, the ring gear torque has a fixed ratio to the generator
torque and the engine torque. As such, the ring gear torque can be
calculated directly from the generator torque according to the
following:
.tau..rho..times..tau. ##EQU00001##
During transient events, both the engine speed and the generator
speed change. An inertia term is usually involved, which makes
equation (1) less accurate, but other methods can be used to
calculate the transient ring gear torque. For example, during a
transient event, the sun gear torque may be calculated based on the
generator torque minus the generator inertia torque. Then the
reflected ring gear torque may be determined according to:
.tau..rho..times..tau..times..omega. ##EQU00002## where J.sub.g is
the lumped moment of inertia of the generator and the sun gear. The
ring gear torque is negative in the steady state based on the sign
convention used here.
The motor torque is calculated to provide the driver's commanded
wheel torque at any ring gear torque output according to:
.tau..sub.m(t)=.rho..sub.m2d.tau..sub.w.sub.--.sub.cmd(t)+.rho..sub.m2p{c-
ircumflex over (.tau.)}.sub.r(t) (3) where
.tau..sub.w.sub.--.sub.cmd is the driver commanded wheel torque and
.rho..sub.m2d and .rho..sub.m2p are gear ratios from the motor to
the wheel and from the motor to the ring gear.
During some transient events, namely engine start/stop and large
variation in the driver torque command, the inaccuracy of the ring
gear torque and large torque ramp rate can excite the driveline
resonant mode(s) and cause undesirable vehicle oscillation if no
adequate counter measure is used to damp the motor torque. A
mechanical damper is cost inefficient and only works within a
narrow bandwidth of the exciting frequency. As such, a logic-based
or software solution is more desirable for this case.
Referring now to FIG. 2, a block diagram illustrates a hybrid
vehicle having a mechanical driveline according to various
embodiments of the present disclosure. In one embodiment, vehicle
100 is an HEV having a power split architecture such as is
illustrated in FIG. 1. The vehicle 100 includes a motor 101,
traction wheels 102, and a driveline 103 that drivably connects the
motor 101 and traction wheels 102, as illustrated by the heavy
line. The driveline 103 has one or more resonant frequencies.
Vehicle 100 also includes a motor controller 104. The motor
controller receives torque requests as signals from other
controllers (not shown). The motor controller 104 controls or is in
communication with motor 101 and wheel speed sensors 105, as
indicated by the dashed line. The motor controller 104 may generate
torque commands and provide the torque commands to the motor 101.
The motor in turn generates the commanded torque and transmits it
to the traction wheels 102 through the driveline 103. One or more
wheel speed sensors 105 may communicate directly or indirectly with
motor controller 104. In various embodiments, wheel speed sensors
105 may be incorporated into an antilock brake system (ABS) that
includes an ABS control module (not shown) in communication with
motor controller 104.
Referring now to FIG. 3, a flowchart illustrates operation of a
system or method for controlling a hybrid vehicle according to
various embodiments of the disclosure. As those of ordinary skill
in the art will understand, the functions represented by the flow
chart blocks may be performed by software and/or hardware.
Depending upon the particular processing strategy, such as
event-driven, interrupt-driven, etc., the various functions may be
performed in an order or sequence other than illustrated in the
Figures. Similarly, one or more steps or functions may be
repeatedly performed, although not explicitly illustrated. In one
embodiment, the functions illustrated are primarily implemented by
software, instructions, code or control logic stored in a computer
readable storage medium and executed by one or more
microprocessor-based computers or controllers to control operation
of the vehicle. All of the illustrated steps or functions are not
necessarily required to provide various features and advantages
according to the present disclosure. As such, some steps or
functions may be omitted in some applications or implementations.
The algorithm for controlling a motor in an HEV according to one
embodiment of the present disclosure as illustrated in FIG. 3
includes steps or functions that may be represented by control
logic or software executed by one or more microprocessor-based
controllers, such as motor controller 104, for example.
As illustrated in FIG. 3, a torque request is received in block
201. The torque request may be in response to a vehicle start event
as illustrated in block 202, or in response to a change in driver
requested torque as illustrated in block 203. A provisional target
torque is generated, as illustrated in block 204. The target torque
is adjusted based on a difference between a measured motor speed
and a calculated vehicle speed, as illustrated in block 205. In one
embodiment, the vehicle speed is calculated based on an average of
wheel speed signals, such as may be received from an ABS module, as
illustrated in block 206. In another embodiment described in
greater detail with references to FIGS. 4 and 5, the vehicle speed
is calculated based on a filtered measured motor speed as
illustrated in block 207, where the filtering is a low pass filter
that removes transients. The target torque is filtered to attenuate
a driveline natural or resonant frequency, as illustrated in block
208. This filtering may be performed using a band stop or notch
filter as illustrated in block 209 or a band pass filter as
illustrated in block 210. A torque command is generated based on
the adjusted and filtered torque, as illustrated in block 211. The
torque command is then provided to the motor, as illustrated in
block 212.
Referring now to FIG. 4, a proportional plus derivative (PD)
control structure is shown that outputs a torque adjustment based
on a measured motor speed and a calculated vehicle speed. The input
to the controller is a calculation of driveline oscillation. This
calculation may be made by using the measured motor speed minus the
vehicle speed calculated from the wheel speed signals, such as ABS
speed signals. Since the vehicle has much larger inertia than the
drivetrain, its speed is less affected by torque oscillation from
the powertrain. The motor speed, however, is affected by torque
changes on the motor and on the engine because of the small
mechanical damping of the driveline. The speed difference used in
the control takes the form
e=.omega..sub.m-.omega..sub.m.sub.--.sub.w (4) where the reflected
wheel speed is calculated by
.omega..omega..omega. ##EQU00003## The left and right wheel speed
signals .omega..sub.l and .omega..sub.r may be communicated by the
ABS control module or other appropriate sensor(s). Equation (4)
represents the speed difference between the motor, which is
upstream of the driveline, and the vehicle wheels, which are
downstream of the driveline.
A backup mechanism is also placed in this algorithm to calculate
vehicle speed. If wheel speed signals are not available or the
signal quality cannot satisfy the control requirement, an
alternative calculation may be used for the wheel speed
calculation, such as:
.omega..sub.m.sub.--.sub.down(s)=F(s).omega..sub.m(s) (6) where
F(s) is a low pass filter selected to remove any fast transients
related to the motor speed itself. This calculation generates an
inferred vehicle speed from the motor speed. Although it is less
accurate, it is available without requiring the signals from any
wheel speed sensors. While this calculation could be used as the
primary method for determining vehicle speed, it is used as a
backup calculation in this embodiment of the control system. The
relationship of the speed signals is illustrated in FIG. 5.
In the representative embodiment illustrated, the PD control has
the following transfer function:
.function..times..times. ##EQU00004## For the driveline system, the
proportional control of the speed difference (4) will introduce an
additional damping effect of the system. The derivative control
will increase the motor inertia.
In addition to the PD controller, a filter is implemented to
attenuate a driveline natural frequency. The driveline dynamics
generally result in a fixed resonant frequency determined by
various system parameters. The resonant frequency has little
variation during vehicle usage, but may vary somewhat from vehicle
to vehicle. Thus a pole cancellation method can be a powerful and
reliable counter measure used in the control system to attenuate
the specific driveline frequency.
The transfer function of a simplified driveline model for a
representative hybrid electric vehicle having a mechanical
driveline can be written as
.function..omega..times..xi..times..times..omega..times..omega.
##EQU00005## which is a second order system with a small natural
damping ratio. One way to remove the oscillation from these less
damped system poles is to cancel them using the control in the
feedforward path as represented by:
.times..xi..times..times..omega..times..omega..times..phi..times..times..-
omega..times..times..times..omega..times..times. ##EQU00006## where
.phi.>.xi.. Controller (9) cancels out the less damped poles of
the driveline natural frequency and introduces a pair of
well-damped poles at another frequency. The selection of values for
.phi. and .omega..sub.n may be determined during vehicle
calibration and development and may vary based on the particular
vehicle configuration.
The controller (9) functions as a band stop filter or a notch
filter. As such, the controller (9) may be tuned to remove the
frequency content related to the driveline resonant frequency so
the closed loop system is more damped in the designated frequency
range.
The PD controller and filter may be placed in different locations
in the control system, as illustrated in FIGS. 6 and 7. In the
embodiment illustrated in FIG. 6, band stop filter 601 is
positioned in the feedforward loop to cancel out the driveline
resonant frequency. It works together with the PD active damping
control 602, placed in the feedback loop, to further increase the
system damping ratio. The active damping control 602 is of a
similar type as illustrated and described with reference to FIG.
4.
As generally illustrated in FIG. 6, the controller controls
traction motor torque in response to a provisional motor torque
that is adjusted based on a difference between the measured
traction motor speed and a calculated vehicle speed that is
filtered to attenuate a driveline resonant frequency using bandstop
filter 601 positioned in the forward path. The calculated vehicle
speed is based on an average of wheel speed signals or may be
determined from an ABS vehicle speed signal.
In the representative embodiment illustrated in FIG. 7, a band pass
filter 701 is used in the feedback path to the PD active damping
control 702 rather than a band stop filter in the feedforward path
as illustrated in the embodiment of FIG. 6. In this arrangement,
band pass filter 701 removes frequency content outside of the range
of interest. This results in the damping effect introduced by the
PD controller 702 being focused around the range of the driveline
natural frequency.
The processes, methods, or algorithms disclosed herein can be
deliverable to/implemented by a processing device, controller, or
computer, which can include any existing programmable electronic
control unit or dedicated electronic control unit. Similarly, the
processes, methods, or algorithms can be stored as data and
instructions executable by a controller or computer in many forms
including, but not limited to, information permanently stored on
non-writable storage media such as ROM devices and information
alterably stored on writeable storage media such as floppy disks,
magnetic data tape storage, optical data tape storage, CDs, RAM
devices, and other magnetic and optical media. The processes,
methods, or algorithms can also be implemented in a software
executable object. Alternatively, the processes, methods, or
algorithms can be embodied in whole or in part using suitable
hardware components, such as Application Specific Integrated
Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state
machines, controllers, or any other hardware components or devices,
or a combination of hardware, software and firmware components.
As can be seen from the various embodiments, the present invention
provides a control system that can increase the robustness of the
motor torque control by removing the driveline resonant frequency
from a motor torque command. This improves the drivability of a
power split HEV.
While exemplary embodiments are described above, it is not intended
that these embodiments describe all possible forms encompassed by
the claims. The words used in the specification are words of
description rather than limitation, and it is understood that
various changes can be made without departing from the spirit and
scope of the disclosure. As previously described, the features of
various embodiments can be combined to form further embodiments of
the invention that may not be explicitly described or illustrated.
While various embodiments could have been described as providing
advantages or being preferred over other embodiments or prior art
implementations with respect to one or more desired
characteristics, those of ordinary skill in the art recognize that
one or more features or characteristics can be compromised to
achieve desired overall system attributes, which depend on the
specific application and implementation. These attributes can
include, but are not limited to cost, strength, durability, life
cycle cost, marketability, appearance, packaging, size,
serviceability, weight, manufacturability, ease of assembly, etc.
As such, embodiments described as less desirable than other
embodiments or prior art implementations with respect to one or
more characteristics are not outside the scope of the disclosure
and can be desirable for particular applications.
* * * * *